1. Field of the Invention
The subject of the invention is a method of preparing xylenes chlorinated in the nucleus, especially 2,5-dichloro-p-xylene, by the reaction of xylenes, especially p-xylene, with chlorine in the presence of a catalyst system.
2. Discussion of the Prior Art
The chlorination of xylenes in the nucleus in the presence of Friedel-Crafts catalysts, generally FeCl.sub.3, is known. For example, in U.S. Pat. No. 2,421,389, the chlorination of p-xylene in the presence of a Friedel-Crafts catalyst and CCl.sub.4 is described, wherein monochloroxylene, 2,3- and 2,5-dichloro-p-xylene, and trichloro-p-xylene are formed together.
For the controlled preparation of a specific product, it is necessary to strive for selective chlorination.
Selective chlorination processes for the preparation of 2,5-dichloro-p-xylene are described in U.S. Pat. No. 3,002,027, German Offenlegungsschrift No. 2,604,277 and German Offenlegungsschrift No. 2,604,278.
In U.S. Pat. No. 3,002,027, glacial acetic acid is used as solvent. This, however, entails disadvantages in the working up of the reaction mixture and in the recovery of the solvent.
In German Offenlegungsschrift No. 2,604,277 organic sulfur compounds are used as co-catalysts in conjunction with FeCl.sub.3 and SbCl.sub.3, which due to their extremely offensive odor involve difficulties in handling and in the working up of the reaction mixture. The antimony and iron sulfides used as catalysts in German Offenlegungsschrift No. 2,604,278 furthermore require very long chlorination times.